Thermodynamic characteristic for correlated flat-band system with quantum anomalous Hall ground state

TL;DR

This paper investigates the thermodynamic properties of correlated flat-band systems with quantum anomalous Hall ground states, revealing a low-temperature transition driven by excitonic excitations that could be experimentally observed.

Contribution

It identifies a unique thermodynamic characteristic of correlated flat-band models with QAH states, highlighting a low-temperature transition not previously characterized.

Findings

Transition from QAH insulator to metal occurs at low temperature

Proliferation of excitonic particle-hole excitations enhances charge compressibility

Transition temperature is much lower than the zero-temperature gap

Abstract

While the ground state phase diagram of the correlated flat-band systems have been intensively investigated, the dynamic and thermodynamic properties of such lattice models are less explored, but it is the latter which is most relevant to the experimental probes (transport, quantum capacitance and spectroscopy) of the quantum moir\'e materials such as twisted bilayer graphene and transition metal dichalcogenides. Here we show, by means of momentum-space quantum Monte Carlo and exact diagonalization, there exists a unique thermodynamic characteristic for the correlated flat-band models with interaction-driven quantum anomalous Hall (QAH) ground state, namely, the transition from the QAH insulator to the metallic state takes place at a much lower temperature compared with the zero-temperature single-particle gap generated by the long-range Coulomb interaction. Such low transition temperature comes from the proliferation of excitonic particle-hole excitations, which "quantum teleport" the electrons across the gap between different topological bands to restore the broken time-reversal symmetry and give rise to a pronounced enhancement in the charge compressibility. Future experiments, to verify such generic thermodynamic characteristics, are proposed.